Although it has been demonstrated that mitochondria contain glycoproteins, little is known of the structure, synthesis and function of the complex, carbohydrate-containing proteins of this important subcellular organelle. We have demonstrated the presence of glycoproteins in rat liver mitochondria and have characterized their submitochondrial location using the plant lectin concanavalin A. In addition, we have used a concanavalin A affinity column in the isolation and purification of the major glycoprotein of mitochondria. Studies are currently in progress to characterize the structure of this glycoprotein and to determine its function within the mitochondrion. In addition we are using this purified glycoprotein to investigate the glycosyl transferases involved in the synthesis of its oligosaccharide side chains and have found that the mitochondrion does not appear to contain the sialyl and galactosyl transferases required for the synthesis of glycoproteins. Our evidence suggests that the glycosyl transferases involved in the glycosylation of glycoproteins destined for the mitochondrion are contained in the Golgi fraction of rat liver. We have carried out similar studies on the glycoproteins of tumor (hepatoma) mitochondria and find that they are markedly deficient in their content of acidic, sialic acid - containing glycoproteins. The Golgi fraction of hepatoma homogenates contains normal levels galactosyl transferase but markedly reduced levels (less than 20% of normal host liver) of sialyl transferase. We are currently pursuing the problems of mitochondrial glycoproteins structure, synthesis and function using normal and hepatoma-derived mitochondria.